Method of deburring workpieces

ABSTRACT

APPARATUS FOR THE ELECTROCHEMICAL DEBURRING OF METALLIC WORKPIECES IN WHICH A DRUM OR ENDLESS BAND FORMS A CONTINUOUSLY DISPLACEABLE SURFACE FOR THE WORKPIECES WHICH, TOGETHER WITH CARBON PARTICLES AND/OR OTHER ABRASIVE PARTICLES, ARE AGITATED IN AN ELECTROLYTE. THE DRUM IS ROTATED ABOUT ITS HORIZONTAL AXIS WHILE A PAIR OF DISKS FORM ELECTRODES CLOSING THE DRUM. WHEN THE ENDLESS BELT IS USED, IT THEN PASSES INTO A VESSEL RETAINING THE ELECTROLYTE AND THEREAFTER CARRYING THE WORKPIECES TO A COLLECTING TROUGH WHILE CARBON PARTICLES ARE CONTINUOUSLY ADDED OR REMOVED FROM THE SYSTEM WHOSE ELECTRODES ARE CONNECTED IN PAIRS TO RESPECTIVE PHASES OF THE POWER SUPPLY.

1973 KIYOSHI INOUE METHOD OF DEBURRING WORKPIECES l3 Sheets-Sheet 1 Filed Feb. 25, 1971 FIG.!

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KIYOSHI INOUE INVENTOR.

Attorney Dec. 4, K|YOSH| |NOUE 3,776,827

METHOD OF DEBURRING WORKPIECES Filed Feb. 25, 1971 13 Sheets-Sheet 2 F a G KIYOSHI INOUE INVENTOR.

Attorney Dec. 4, 1973 KlYOSH] |NOUE 3,776,827

METHOD OF DEBURRING WORKPTECES Filed Feb 25, 1971 13 Sheets-Sheet :5

K I YO SHI INO U E INVENTOR.

Attorney Dec. 4, K|YOSH| |NOUE 3,776,827

METHOD OF DEBURRING WORKPTECES Filed Feb. 25, 1971 13 Sheets-Sheet 4 KIYOSHI INOUE INVENTOR.

Attorney Dec. 4, 1973 K|YO$H| |NOUE 3,776,827

METHOD OF DEBURRING WORKPIECES Filed Feb. 25, 1971 13- Sheets-Sheet 5 KIYOSHI INOUE INVENTOR.

Atiorney Dec. 4, 1973 KIYOSHI INOUE 3,776,827

METHOD OF DEBURRING WORKPTECES Filed Feb. 25, 1971 1:5 Sheets-Sheet 6 Isl? - KIYOSHI moue INVENTOR.

Attorney Dec. 4, 1 973 K|YOSH| |NQUE 3,776,827

METHOD OF DEBURRING WORKPTECES Filed Feb. 25, 1971 13 Sheets-Sheet 7 FEG.IO

7- KIYOSHI INOUE INVENTOR. m9

BY 3w WA ATTORNEY DQ 1973 KIYOSH! INOUE 3,775,327

METHOD OF DEBURRING WORKPTECES Filed Feb. 25, 1971 13 Sheets-Sheet E F l G H l8l9 l8l8 u Q 3 w 9625 E l8|0b KIYOSHI INOUE INVENTOR.

ATTORNEY Dec. 4, K|YO5H| lNQUE 3,776,827

METHOD OF DEBURRING WORKPTECES Filed Feb. 25, 1971 V13 Sheets-Sheet n PEG-J5 l9l8 y ZOII/ZOB 2OIO 20|Ob KIYOSHI INOUE I N VEN TOR.

BY S

ATTORNEY DEC. 4, KIYOSH] |NOUE METHOD OF DEBURRING WORKPTFICF-S Filed Feb. 25, 1971 13 Sheets-Sheet i0 Deburring speed (Removal roie grams 50 I Sminutes 20 A fl a r I I I I n I I r O,| 0,5 l 2 5 IO 20 50 I00 Volume ratio (Conduciive particles workpieces KIYOSHI INOUE INVENTOR.

ATTOR NEY 1973 KIYOSHI INOUE METHOD OF DEBURRING WORKPTF-CES l3 Sheets-Sheet 11 Filed Feb. 25, 1971 Fae KIYOSHI INOUE I N VEN TOR.

ATTORNEY 1973 KIYOSHI INOUE 3,776,827

METHOD OF DEBURRING WORKPIECES Filed Feb. 25, 1971 15 s t s 12 KIYOSHI INOUE INVENTOR.

ATTORNEY United States Patent vs. Cl. 204-12946 16 Claims ABSTRACT on THE DISCLOSURE Apparatus for the electrochemical deburring of metallic workpieces in which a drum orendless band forms a continuously displaceable surface for the workpieces which,.together with carbon particles and/or other abrasive particles, are agitated in an electrolyte. The drum is rotated about its horizontal axis while a pair of disks form electrodes closing the drum. When the endless belt is used, it then passes into a vessel retaining the electrolyte and thereafter carrying the workpieces to a collecting trough while carbon particles are continuously added or removed from the system whose electrodes are connected in pairs to respective phases of the power supply.

( l) CROSS REFERENCE TO EARLIER APPLICATIONS I This application is a continuation-in-part of copending application Ser. No. 714,252, filed Mar. 19, 1968 (now Pat. No. 3,620,953), as a continuation-in-part of then pending application Ser. No. 598,391, filed Dec. 1, 1966, now abandoned and replaced by continuation application Ser. No. 859,532, filed Apr. 21, 1969, now US. Pat. No. 3,533,928, issued Oct. 13, 1970.

(2) FIELD OF THE INVENTION My present invention relates to a method of and an apparatus for the deburring of metallic and other conductive workpieces whereby surface irregularities of such workpieces can be eliminated.

(3) BACKGROUND OF THE INVENTION Deburring apparatus of several types are commonly in usein the metal-Working field, primarily for the removal of surfaceirregularities in cast, machined and molded metallic workpieces. For the most part, such apparatus includes a tumbling drum provided with agitating means for repeatedly casting the workpieces, generally in a liquid vehicle and sometimes in the presence of an abrasive, into contact with one another, against the walls of the vessel ors drum or into contact with other bodies .(e.g. of abrasive material) mixed with the charge in the drum. This tumbling action mechanically dislodges adherent materials while rounding off irregular portions and projections integral withthe metallic bodies. These systems, however, are relatively slow and even defective when the deburring operation is to remove substantial amounts of material.

(4) OBJECTS OF THE INVENTION tively simple and inexpensive apparatus for a high rate deburring of metallic workpieces while yielding a relatively high quality surface finish.

Yet another object of this invention is to provide a method of and an apparatus for the deburring of relatively large-dimension workpieces of such nature that tumbling may be impractical.

(5) SUMMARY OF THE INVENTION These objects and other which will become apparent hereinafter are attained, in accordance with the present invention, by a method of deburring metallic workpieces in which the liquid vehicle is agitated in contact with the workpiece to be deburred while mechanical contact between the surfaces of the latter and at least some other bodies is carried out concurrently with an electrochemical material-removal step.

As set forth in application Ser. No. 598,391, which eventually matured into US. Pat. 3,533,928, I have found, surprisingly, that electrochemical techniques hitherto used primarily for the electrochemical machining (ECM) and electrochemical grinding (ECG) of metallic bodies, wherein close tolerances are a necessity, can be used effectively in conjunction with a tumbling or agitating.

operation to debur metallic workpieces or objects having electrolytically soluble surface portions. The surprising nature of this discovery will become all the more apparent when it is recognized that the present method does not require a stationary electrode urged against the workpiece or juxtaposed therewith via a predetermined ma chining gap.

In accordance with the principal feature of this invention, an electrochemical machining current, which may be direct or periodic (e.g. raw-rectified alternating current, pulsating direct current and ordinary AC) is passed through the liquid vehicle which is constituted as an electrolyte and may contain abrasive particles or merely additional bodies to facilitate mechanical deburring of the workpieces concurrently with the electrochemical action. While, in some cases, the workpiece may be stationary and is connected with a pole of the electrochemical machining sources, I have found that it is not necessary to connect the workpieces directly thereto, and that the mere tumbling of such workpieces in an electrolyte and in a drum having spaced-apart contact portions bridged by the electrolyte but not shortcircuited by the drum itself, can effect electrochemical removal of material from the workpiece surfaces.

While I do not wish to be bound by any theory in this regard and the precise reasons why the current flow through the electrolyte is effective to remove material from the surfaces of the conductive workpieces are not yet clear, it may be hypothesized that each of the workpieces acts as an electrode, for the machining of others or as objects undergoing electrolytic erosion against other conductive bodies. Since electrolytic oxidation of the workpiece at its surface is essentially nonreversible in the sense that agitation and mechanical action of the elec were directly connected to each workpiece.

According to a more specific feature of this inven tion, the agitation of a multiplicity of workpieces is eff'ected in a'tumbling drum which may be provided. at its base with one electrode portion and with a second contact or electrode, at .a location spaced therefrom but in,

contact with the electrolyte, the electrodes being connected across an AC' or DC electrochemical-machining source, eagj of th'e 'type described -and illustrated in any of the applications Ser. No. 512,338 (US. Pat. No. 3,475,312), Ser. No. 535,268 (U.S. Pat. No. 3,417,006), Ser. No. 562,857 (U.S. Pat. No. 3,420,759), filed Dec. 8, 1965, Jan. 19, 1966 and July 5, 1966, respectively, all of which were pending at the time the parent application was filed. The tumbling drum can be upwardly open and rotatable about an axis tilted upwardly at an angle of, say, 30 degrees from the horizontal. In this case, the agitation is effected purely by rotation of the drum.

I have also found it to be possible, in conjunction with such a tumbling drum, or when a stationary vessel is employed, to effect the agitation at least in part by magnetic means. Thus, if the workpieces treated in the deburring operation or the other bodies involved are magnetically permeable, I apply a magnetic field to them so as to effect their displacement in the electrolyte; I also may distribute in the deburring vessel among the workpieces particles or bodies of a magnetically permeable material. Such bodies may be abrasive or electrically conductive to facilitate electrochemical erosion of the workpieces or produce the friction necessary for the deburring action. In fact, the particles or bodies serving as the agitating means need not be magnetically permeable under some circumstances, since the particles in the electrolyte tend to respond to a rapidly changing magnetic field by rotating about the axis thereof. Thus, agitation may be promoted with the aid of conductive as well as magnetically permeable particles. According to still another feature of this aspect of the invention, the particles which are magnetically or electrically displaceable in the liquid vehicle, can be coated with abrasive material, incorporated in or mixed with abrasive particles which are not influenced by an electromagnetic field.

Preference is given, in accordance with this invention, to pulsating or alternating electromagnetic fields for controlling the movement of particles and inducing electrochemical erosion of the workpiece surfaces since purely direct current has a tendency to produce agglomeration of magnetic particles in the deburring vessel.

According to another aspect of the basic concept, the agitation is carried out by rotating an electrode immersed in the electrolyte by, for example, rotating an electrode member in an irregular die cavity to deburr the machined surfaces thereof. Abrasive particles are here included in the deburring vehicle while an eltctrolytic machining current is applied between the workpiece and this rotating element. In asmuch as this electrode member is not closely juxtaposed with the workpiece surface and is rotated relatively rapidly, a more or less uniform surfacing is effected. In accordance with this aspect of the invention, I prefer to incorporate in the vehicle a multiplicity of conductive particles which here act as intermediate electrodes and as they are dispersed by the agitation into the rotation of the die surfaces, each particle acts as an individual electrode to facilitate smoothing of the die surface. The rotary electrode member imparts a centrifugal forces to the abrasive and conductive particles contained within the electrolyte so that these particles are dynamically urged outwardly and forcefully brought into contact or close juxtaposition with the surfaces to be treated to augment the resulting mechanical deburring action.

According to yet another aspect of this invention, deburring is carried out as augmented by a magnetic-field pressure which, when combined with the dynamic flow of rapidly moving particles, with the centrifugal force of tumbling or electrolyte displacement by a stirrer and with gravitational forces, magnetically urges the abrasive bodies against the workpieces and the workpieces against one another. This magnetic field pressure is, advantageously, supplied by electromagnetic means disposed externally of the deburring vessel and capable of applying inward magnetic forces to the magnetically permeable particles and workpieces. When the abrasive particles or au y d e savi t9 te i ita e me ha ic l rem val 4 of irregularities and projections upon the workpieces are magnetically permeable and/or the workpieces are of such permeability, a high frequency magnetic field applied from without, in accordance with this invention, induces an oscillation and/or a magnetostrictive expansion and contraction of the bodies so that the simple tumbling action is accompanied by a magnetic vibration or pulsation of the body to improve the erosive operation. In this connection it can also be stated that the field may be of such nature that vibration of the individual particles by the magnetic field is coupled with a tumbling action of a rotary drum or a vibration thereof to increase the mechanical abrasion.

Another feature of this invention resides in the use of chemical action in removing surface irregularities in combination with the electrochemical and mechanical deburring action as described above. Thus I have found that surprisingly effective results can be obtained when a chemical mordant or etchant for the workpiece material is incorporated in the electrolyte. For as yet unknown reasons, the surface finish and deburring rate obtained when, for example, ferric chloride is used as the chemical etchant in the electrolyte, is better than that which would be expected with either the etchant or the electrochemical action alone, while the rate of material removal exceeds the sum predictable from the individual actions of the etchant and the electrochemical erosion.

According to a further feature of the present invention, the electrochemical deburring of metallic workpieces is carried out concurrently with agitation of the bodies in an electrically nonconductive tumbling drum rotatable about a recumbent axis (preferably horizontal or near horizontal) containing liquid electrolyte and the conductive (i.e. carbon) particles, together with the workpieces as described therein. A pair of electrodes are in constant contact with the electrolyte during rotation of the drum and are preferably disposed at remote ends of the electrolyte bath and are composed of a material insoluble in the electrolyte and free from electrolytic attack thereby. I have surprisingly found that excellent results can be attained when the conductive electrodes are constituted by the end walls of the drum and rotate therewith, the cylindrical drum wall forming the insulating spacer for these electrodes. At least one but preferably both of these end walls are provided with a passage for circulating the electrolyte through the drum, the axial passage terminating in a fan-like array of bores opening into the drum at the face of the end wall contacting the electrolyte. The drum may further be provided, at least at regions extending above the electrolyte level therein, with apertures or vents enabling evacuation of the gaseous products of the electrolytic deburring of the workpieces.

Still another aspect of this invention resides in my discovery that irregular deburring can be avoided by injecting an inert gas into the electrolyte bath with the recirculating electrolyte stream. It appears that the inert gas creates la'byrinthian paths for the electric current flowing through the electrolyte, i.e. the ion-mobility paths, thereby distributing the electrochemical action substantially uniformly. This technique has the additional advantage that the inert gas upon evolution from the electrolyte acts as a diluent for the nascent gases generated by electrolysis and led off through the vents above the electrolyte level. The inert gas may be admixed with the electrolyte in the bath or with the liquid prior to its introduction into the tumbling drum. Furthermore, in accordance with the principles already discussed above in general terms, I provide a magnetic flux radially through the drum, i.e. vertically when the drum is horizontal, preferably at a location intermediate the electrode, to facilitate the agitation of the electrolyte, the workpieces, and the carbon particles forming intermediate electrodes for the deburring action. These carbon particles have an abrasive or semiabrasive character so that they mechanically co-operate with the workpieces to supplement the electrochemical deburring by mechanical erosion of the rough, surfaces. Thus the carbon particles may be carbonaceous materials of relatively high hardness (e.g. synthetic diamondas produced by the system described in my U.S. Pat. No. 3,207,58 2;or the nondiamond but highhardness carbon particles obtained when synthetic diamond is made in accordance with that process).

Further investigations into t'he phenomenon described above, i.e. the ability of conductive particles to act as secondary electrodes when an electric current is applied across the electrolyte to solubilize portions of the workpiece surface, have demonstrated that the volume ratio of the workpieces and the conductive particles in a deburring system, is important.

More specifically, I have found that there is a tendency with large ratios of total workpiece volume to total conductive-particle volume, for electric discharges to occur between the workpieces and damage the surfaces of the latter, in spite of the fact that these workpieces are randomly distributed in the electrolyte/conductive particle system.

' I have also discovered that it is possible to avoid such electrical discharges by providing a large proportion of conductive particles so that the volume ratio of the workpieces to the conductive particles ranges between 1:1 and 1:20. The term volume ratio as used herein is intended to refer to the bulk volume as measured by cascading the workpieces and'the particles, respectively, into confined spaces. Within this range, a qualitative improvement of the deburring process is observed. In addition I have found that there is a relationship between deburring effectiveness and the relative sizes of the workpiece and the conductive particle. Here it should be noted that the conductive workpieces tobe deburred will generally be of uniform size and shape, they being derived from a system for the mass production ofv such workpieces. Similarly, the conductive particles will generally be of a uniform size and shape. In this connection, it has been found to be advantageous to provide a conductive particle having a volume ranging between A to 3 times the volume of the individual workpiece and, where workpieces of different size or shape are used, the average volume of the workpieces. In this case, the actual volume occupied by the workpiece or the particle is the quantity of interest.

Consistent with the foregoing discussion, is the fact that the process of the present invention is often best carried out in a relatively small quantity of electrolyte so that an intimate relationship between the workpieces, conductive particles and electrolyte is assured. The volume of the conductive particles may make up the major fraction of the electrolyte/ conductive particle system. Hence, the volume of the conductive particles may exceed the volume of the electrolyte.

The present invention also contemplates the provision of means for compensating the system or depletion of the electrolyte by evaporation or decomposition, either to permit control of the electrolyte in accordance with the principle thus enunciated or simply to maintain the electrolyte in as close to its original condition as possible. I may provide, therefore, a pair of electrodes in contact with the electrolyte and connect the latter to a source of electric current and to a current-responsive sensor for operating a valve system adapted-to introduce additional quantities of electrolyte into the vessel upon 'an increase in the electrolyte concentration or simply a reduction in the electrolyte level representing a loss of'electrolyte.

Advantageously, the system includes mechanical vibrating means which, as described earlier, not only serve to agitate the workpiece in contact with the electrolyte, but also co-operate with an upwardly extending helical or spiral channel along which the electrolyte, conductive particles and workpieces are advanced between the electrodes. At the upper portion of the helix, the workpieces may be separated from theelectrolyte which can return 6, to the vessel. Additional electrolyte may be provided at any point along the helical path at which depletion is detected in the manner set forth above or at the beginning of said path. In order to facilitate advance of the workpieces along the upwardly inclined helical transport path, I may mount the vessel resiliently and provide vibrating means such that a rotation or angular vibration is provided in addition to an axial or vertical vibration.

I have found it to be advantageous, moreover, to provide support means for the workpiece aside from the ramp discussed above which imparts an angular velocity to the workpieces or to the system of conductive particles. For example, the workpiece may be held stationary in a suitable holder while the entire electrolyte/conductive particle system is spun or rotated around the holder.

I may also mention that, although a number of electrolytes have been found to be suitable, certain compositions have more recently been discovered to have unusual results. For example, it has been observed that for relative rough deburring operations, the electrolyte should include Percent by weight Sulfuric acid 30-70 Glycerine 20-60 Balance water.

Percent by weight Sulfuric acid 30-70 Fluoboric acid 5-25 Oxalic acid 0.5-1.5 Balance water.

Percent by weight Phosphoric acid 70-90 Gelatin 0.5-10

Balance water.

For copper and copper alloy workpieces, the following electrolyte has been found to be effective:

Percent by weight Sulfuric acid 40-60 Acetic acid 5-15 Chromic acid 5-15 Balance water.

For aluminum and aluminum alloy workpieces, the following composition has been found to yield. the best electrolyte: i

p a Percentby weight Sodium carbonate 10-20 Sodium phosphate .Q. 2-10 Glycerine 40-60 Fluoboric acid and/or ammonium borofiuoride Balance water.- v.

-F0r tungsten and tungsten alloy workpieces, the most suitable electrolyte ,is: v 7

Percent by weight: Nitric acid I 15-30 Hydrogen fluoride u Balance phosphoric acid.

For metal-carbide workpieces, the following electrolyte has been found to be effective:

Percent by weight Ferric chloride 40-60 Hydrogen chloride 0.5-2

Balance nitric acid.

Each of the compositions (a)-(g) may include up to 2% of one or more of the following finishing and brightening compounds:

sodium oleate sodium laureate sodium stearate sodium palmitate sodium alkyl sulfonate where the alkyl group has from 6 to 22 carbon atoms in the carbon chain and sodium alcohol-ester sulfates where the alcohol group has a carbon chain with 6 to 22 carbon atoms.

(6) DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial crosssectional view through a tumbling drum of a deburring apparatus in accordance with this invention;

FIG. 2A is an axial cross-sectional view of an electrode forming an end wall of the drum;

FIG. 2B is an elevational view thereof;

FIG. 3A is a cross-sectional view through a modified electrode;

FIG. 3B is an elevational view of this latter electrode;

FIG. 4 is a diagram of the electrochemical deburring system of the present invention;

FIG. 5 is a view similar to FIG. 1 of a modified system for deburring metallic workpieces;

FIG. 6 is an axial cross-sectional view through a tumbling system embodying other principles of this invention;

FIG. 7 is a diagram of a continuous deburring apparatus in accordance with the principles of this invention;

FIG. 8 is an axial cross-sectional view through a deburring apparatus uising a stationary system and diagrammaticaly showing the electrolyte-circulating means therefor;

FIG. 9 is a cross-sectional view along the line IX-IX of FIG. 8;

FIG. 10 is a diagrammatic cross-sectional view of a vibratory apparatus for deburring workpieces;

FIG. 11 is a diagrammatic perspective view of another apparatus embodying the invention;

FIG. 12 is an axial cross section through the latter vessel;

FIG. 13 is an elevational view of the vi-bratile mounting of the vessel;

FIG. 14 is a cross-sectional view illustrating the electrolyte supply to the latter vessel;

FIG. 15 is a diagrammatical vertical section through another embodiment of the invention;

FIG. 16 is a diagrammatical section through an apparatus illustrating a feature of the invention wherein the workpieces are held stationary and the electrolyte-conductive particle system rotates;

FIG. 17 is a graph illustrating further features of the instant invention;

FIG. 18 is a vertical cross-sectional view of an apparatus according to another embodiment of the invention wherein the workpieces are supported in the electrolyte by suspension;

FIG. 19 is a vertical cross-sectional view of an apparatus according to the invention using magnetic s pp of the workpieces;

FIG. 20 is an axial cross-sectional view of a tumbling apparatus having another arrangement of the electrodes;

FIG. 21 is a cross section taken along the line XXI- XXI of FIG. 20;

FIG. 22 is a cross-sectional view through one of the electrodes of FIGS. 20 and 21 in another embodiment;

FIG. 23 shows a modified electrode;

FIG. 24 is a section similar to that of FIG. 20 but illustrating another arrangement of the drum;

FIG. 25 is a section generally along line XXVXXV of FIG. 24; and

FIG. 26 is a view similar to FIG. 25 illustrating another embodiment of the invention.

(7) SPECIFIC DESCRIPTION In FIG. 1, I show a rotary tumbling system for the deburring of metallic workpieces in which a closed drum 1010 has a pair of end walls 1017 and 1018 forming electrodes and retaining the electrolyte 1011 in the drum. Between the conductive electrodes 1017 and 1018, the drum is formed as a nonconductive sleeve 1040 composed of or lined with electrically insulating material such as a hard rubber or an electrolyte-resistant synthetic resin (e.g. a polyacrylate). Electrically insulating rubber gaskets 1042 are provided between the drum body 1041 and the electrodes 1017 and 1018. The drum may also be formed with a door 1045 to permit the workpieces and intermediate electrodes to be introduced into the interior of the drum. The electrodes 1017 and 1018, which are inert to the electrochemical action and to the electrolyte, are composed of graphite or an insoluble metal (e.g. stainless steel or Monel). The drum 1010 is mounted upon a pair of trunnions 1024a and 1024b extending upwardly from a base and defining for the drum a horizontal axis. The drum is, in turn, carried by a pair of tubular shafts 1023a and 1023b affixed to the respective electrode end walls 1017 and 1018 as described in connection with FIGS. 2A, 2B and FIGS. 3A, 3B.

The drive means for the drum comprises a motor 1027 whose output shaft 1028 is connected by a V-belt transmission 1030 with the hollow shaft 1023a to rotate the drum about its horizontal axis. The electric current for the electrochemical deburring operation i provided by a power supply 1019 and is applied via a pair of brushes 1019a and 1019b to the electrodes 1017 and 1018 via their shafts 1023a and 1023b. Electrolyte is circulated through the drum by a pump 1039 and a circulating system including an inlet pipe 1040 connected with the tubular shaft 1023b. The tubular shaft 1023a leads electrolyte from the drum to a return tube 1043 ending at a reservoir 1044.

The electrode 1017 and 1018 may be provided with a fan-shaped array of bores (FIGS. 2A and 2B) or a central array of mutually parallel bores (FIGS. 3A and 3B), while mean may be provided for injecting a gas into the liquid-circulating stream (FIG. 5) and a magnetic field may be applied in the radial direction (FIGS. 5 and 6). In the embodiment illustrated in FIG. 1, however, the end walls and electrodes 1017 and 1018 are provided with axially extending bores 1017' and 1018 communicating with the hollow shafts 1023a and 1023b, respectively.

Within the drum I provide, in addition to the electrolyte 1011, a mass of metallic workpieces [1012 (shown as rectangles) accompanied by conductive particles 1013 (hatched circles) and, if desired, magnetic and abrasive particles as described in US. Pat. 3,533,928. The electrolyte may be any of the electrochemical machining solutions described in Pats. 3,475,312, 3,417,006 and 3,420,759.

While any of the aforedescribed electrolytes has been found to be more or less effective for the deburring of metallic workpieces, certain electrolytes perform optimally with certain workpieces. For example, for iron and other ferrous-metal workpieces I prefer a composition of 30 to 70% by weight sulfuric acid and. 20 to 60% by Weight glycerine or to 25% by weight fluoboric acid, the latter being used with 0.5 to 1.5% by weight oxalic acid. An alternative is a composition containing 70 to 90% phosphoric acid and a small amount of gelatin. Thebalance is water in all cases and the composition may include brighteners or finishing substances such as the sodium salts of the fatty acids, the sodium alkyl sulfonates and the sodium alcohol-ester sulfates mentioned earlier.

' The particles 1013 are composed of carbon and act as intermediate electrodes. An important aspect of this inv'ention resides in the fact that the carbon particles are formed of-relatively high hardness carbonaceous material capable of withstanding metallic abrasion in the tumbling of the workpieces. Suitable particles may be made by sintering pyrolytic carbon or by the electricdischarge technique set forth in my Pat. 3,207,582. In addition, the carbon particles may contain silicon carbide or the like abrasive powder dispersed therein prior to sintering. As a result, the electrochemical action is augmented by a mechanical smoothing of the workpieces concurrent with electrochemical removal of projecting portions of the workpieces (i.e. burrs). The deburring power supply 1019 may be any electrolysis source as described in US. Pat. 3,533,928. Suitable sources may be alternating current, pulsating direct current or filtered direct current as there described.

EXAMPLE I Using the system of FIG. 1, deburring was carried out in a 15% sodium chloride solution upon a mass of 35% by volume of steel workpieces having a diameter of mm. and a length of 5 mm. Conductive particles, i.e. sintered pyrolytic graphite and silicon carbide particles with a diameter of about 5 mm. were used in a ratio to the workpiece quantity of about 1.15:1; it was possible to increase the deburring rate over conventional systems using only aluminum oxide abrasive particles and a similar drum (diameter 300 mm., axial length of 7 mm., electrolyte quantity 5 liters, current 80 amp.), in terms of the quantity of material removed per unit time, from 10 to 30 times, and to obtain an improved surface finish. In FIGS. 2A and 2B, I show a modified version of the terminal electrode for the drum of FIGS. 1, 5 and 6, the electrodes 1117 generally comprising a disk 1117a of graphite of other electrochemically inert material attached at a flange 1117b to the tubular shaft 1123. A fanlike array of bores 11170 is formed in the disk 1117a and open at the'inner face 1 117d in contact with the electrolyte withinthe drum. From FIG. 2B it is apparent that the bores are distributed in conical arrays about axis of rotation of the drum (represented at 1125) so that a number of "these bores open into the drum above the liquid level (see FIG. 1) at each of the electrodes 1017 and 1018. Thus gas forming above the electrolyte bath can pass through the uppermost bores and can be entrained with the liquid stream leaving the drum and flowing to thereservoir 1044. In this reservoir, which is open to the atmosphere, the gases entrained in the liquid can evolve into the atmosphere. The fanlike array of bores has the additional advantage that, at the inlet electrode- (eg. electrode 1018), the bores disperse the liquid and anygases entrained therein (FIGS. 5 and 6) to insure fine distribution of gas bubbles in the electrolyte bath and even deliver some gas above the electrolyte to act as a diluent for the electrolytically evolved gases. The bores 1117c converge axially away from the drum to communicate with the'tubular shaft 1123 and thus form a manifold.

' Electrode 1217 of FIGS. 3A and 3B represents a modified construction in which the disk 1217a is formed with a plurality of mutually spaced parallel bores 12170 which are located in the region of the center of the disk and communicatingv with the hollow shaft 1223 which is attached to the" disk 1217a at a flange 1217b. This em- 10 bodiment has the dispersing advantages mentioned in connection with the electrodes of FIGS. 2A and 2B but does not evacuate gases from above the electrolyte level as effectively. Either of the electrodes of FIGS. 2A and 2B and of FIGS. 3A and 3B can be used in the drum deburring systems of FIGS. 1, 5 and 6.

In FIG. 4, there is shown a diagram of the principles of the present invention. In this figure, I show the workpieces 1012 as fortuitously located between a pair of carbon particles 1013 and the electrodes 1017 and 1018. If electrode 1017 is positive as shown for the purposes of the explanation of this electrochemical phenomenon, it will be seen that a proximal carbon particle 1013 received an inducted charge so that its region juxtaposed with surface 1012 in the electrolyte 1011 acts as an electrode to sustain electrochemical machining of this workpiece surface. The random distribution of conductive particles and workpieces between the electrodes is effective to insure practically uniform electrochemical treatment of all workpiece surfaces.

However, burrs or other projections invariably lie at shorter distances from one of the terminal electrodes or an effective intermediate electrode than the other portions of the surface from which they project. The electrochemical machining current density is substantially higher at these protuberances and machining preferably occurs in these regions. Any mechanical smoothing is cumulative to the electrochemical action. It will be appreciated also that the presence of gas bubbles in the electrolyte augments the machining action and its specific attack upon protuberances and the burrs. It has been found that the gas bubbles tend to adhere to the surface of the workpiece in regions between the burrs and effectively insulate these regions while increasing the current density at the burrs. This, too, improves the surface finish and can be controlled by injecting inert gases into the system as will be described in connection with FIG. 5. The term inert, however, must be construed in terms of the activity performed here. When the evolved gases include hydrogen, it will not be advisable to add oxygen and vice versa. Even normally active gases may be considered inert if they are nonexplosive when used in the presence of gases evolved from the deburring bath.

In FIG. 5, there is shown a horizontal drum 1310 with a central body 1341 held between a pair of gaskets 1342 and electrodes 1317 and 1318 of the type shown in FIGS. 2A and 2B. The electrodes are carried between the tubular shafts 1323a and 1323b whose slip rings are in contact with brushes 1319b and 1319a of the electrochemical machining power supply 1319. A motor 1327 drives the drum about its horizontal axis while electrolyte is circulated through the drum via a pump 1339 from the reservoir 1344 and a line 1340 communicating with hollow shaft 1323b. The electrolyte from the drum is returned via line 1343' to the reservoir.

In accordance with the principles of the present invention, gas is injected into the electrolyte prior to its passage into the drum, the gas-supply source being shown at 1350 in FIG. 5. The source is a tank of air, argon,- carbon dioxide, nitrogen or the like which is connectedvia a valve 1350a and a line 1350b with the hollow shaft 1323b of electrode 1318. When the gas is forced under high pressure into the electrolyte which, in turn, is under pressure of pump 1339, the liquid/ gas mixture entering the drum through the electrode 1318 expands to evolve the gas in the form of bubbles and, in part, to induce some of the gas into the drum above the electrolyte, thereby diluting the nascent gases released by electrolysis. The gas bubbles within the electrolyte adhere'to theworkpiece surfaces and augment the deburring action. An electromagnet 1315, whose flux can be represented by arrow 1 is provided beneath the drum 1310 and is effective to increase the electrochemical machining action.

The magnetic field may be of unidirectional or alternating type while the magnet itself may be stationary or reciprocating. The magnet may be energized by a high-frequency AC source in addition to a low-frequency vibrating or oscillating source. The high-frequency source preferably operates at 400 kHz. to 50 kHz. and end above sonic frequencies while the low-frequencies source operates at, say, 30 to 40 Hz. It appears that the magnetic field has a two-fold action whereby it induces a dynamic flow of liquid electrolyte and secondly, imparts magnetically attractive or repulsive motions to the workpieces when they are permeable.

In the system of FIG. 6, the drum 1410 has a cylindrical body 1441 which is perforated to evolve gases and permit electrolyte to enter the drum as the latter is rotated in a bath 1435. A hood 1451 overlies the bath 1435 and collects the evolved gases. Here too, the tumbling drum 1410 has a pair of disk-shaped electrodes 1417 and 1418 which are insulated from each other by the gaskets 1442 although the electrodes are here not perforated. Nontubular shaft 1423a and 1423b rotatably support the drum 1410 in a pair of trunnions 1424a and 1424b. The drive means is constituted by a motor 1427 and a V-belt transmission 1430 connecting this motor with shaft 1423a. An electrolysis power supply 1419 applies electric current to the electrodes 1417 and 1418 by the brushes 1419a and 1419b. A magnetic field is applied, as previously describe, by the coil 1415 in the vessel 1435.

FIG. 7 shows a continuous system for the deburring of metallic workpieces wherein a succession of workpieces is deposited from a hopper 1552 upon a belt 1553 which directs these workpieces to a perforated endless belt 1510 which functions similarly to the drum of the preceding embodiments. The endless belt 1510, which has horizontal stretch 1510a receiving the workpieces 1512 from the conveyor 1553, passes over an idler pulley 1510b into the electrolyte bath 1511 in a vessel 1535 of funnel-shaped construction prior to emerging from the bath over a further pulley 1510c. Within the vessel 1535, I provide agitating means in the form of an electromagnet 1537 which vertically displaces an armature 1530 against a pair of compression springs 1538a to jumble the workpiece and carbon particles contained on the stretch 1510d of the belt passing through the electrolyte bath. The armature 1538 carries a number of rollers 1538b which support the belt in this region without frictionally impending its movement.

Upon leaving the electrolyte bath 1511, the conveyor 1510 has a horizontal stretch 1510e overhanging a collecting receptacle 1554 in which the deburring workpieces are caught, the band being then returned to the horizontal stretch 1510a by downward stretch 1510 a horizontal stretch 1510q and a vertical stretch 151011.

Intermediate electrodes are formed by a mass of carbon particles 1513 as previously described. The carbon particles are retained in a supply trough 1555 and are carried by a bucket conveyor 1556 to the 'vessel 1511 where they are deposited upon the mass of workpieces entering the bath. The band 1510 is, as previously indicated, perforated and has openings through which the carbon particles may pass as they settle from the electrolysis zone. Thus, carbon particles which settle through the belt 1510 are discharged at an outlet 1543 of the vessel and are collected upon a sieve conveyor 1557 which carries them to the trough 1555. The electrolyte passing through the sieve conveyor 1557 is collected in the reservoir 1544 and recirculated by a pump 1539 and a line 1540 to the bath 1511.

The electrodes may comprise vertical rods 1518a, 1518b and 1518c which can be angularly oscillated about respective vertical axes and vertically reciprocated by the mechanisms shown for similar electrodes in the lastmentioned application. I have found, moreover, that improved power utilization can be obtained when a. polyphase power supply is available and the number of electrodes is equal n P where P is the number of phases (usually three) available at the supply and n is an integer. In this system, each phase is applied between one pair of electrodes or the corresponding electrodes of a pair of sets, each set having it electrodes. In the simplified system of FIG. 7, the power supply comprises a threephase source 1519a which supplies a conventional Y or A transformer diagrammatically represented at 1519b each of the output faces of which is applied across a pair of the electrodes 1518a through 15180. The connections to these electrodes are shown both for Y and A systems although it will be understood that only one of these systems may be in use at any time. In the Y system, the neutral pole may be grounded at the transformer. This arrangement permits each phase of a three-phase current to be effective and provides a greater effectiveness of the supply power without the expense rectifier systems which would be necessary to produce direct current and the complex circuitry which would be necessary to convert the three-phase force current to single-phase balanced current in operating the deburring device. It has been found that the system is particularly desirable when a large number of workpieces with a relatively large total volume is to be deburred at one time.

In FIGS. 8 and 9, I show another embodiment of the present invention in which no continuously displaceable endless surface is provided and the agitation of the electrolyte, carbon particles and workpieces, is carried out by means of pulsed jets or high-velocity streams of electrolyte directed tangentially into the vessel at the deburring region. This system, while atfording some mechanical smoothing by contact of the workpieces with the carbon particles and the electrodes and walls of the vessel, primarily is effective to promote electrochemical removal of material from the workpiece surfaces without any movable apparatus members. The freedom of this system from vibrational and rotational movement of electrodes, containers and the like eliminates the need for drive motors, journaling assemblies and the like, thereby making the entire apparatus more practical and less expensive, especially where small quantities of workpieces are to be treated.

In accordance with the principles of the present invention, the apparatus comprises a stationary vessel 1610 of electrically insulating material having an upwardly open pot-shaped chamber 1643 with an accurately concave bottom 1643a. A pair of electrodes 1617 and 1618 disposed at diametrically opposite locations along the inner wall of the chamber and energized by an electrochemical machining deburring power supply 1619 of the character previously described. The vessel contains an electrolyte 1611 in which the workpieces 1612 (diagrammatically shown as rectangles) and carbon particles 1613 (diagrammatically shown as circles) are distributed. The carbon particles 1613 are composed of sintered carbon to which abrasive powder has been added and may be used in conjunction with abrasive particles which contain no conductive material. When a number of pairs of electrodes are provided in this system, the considerations discussed in connection with FIG. 7 apply and the power supply may include a polyphase-current source each phase of which is connected across a respective pair of electrodes or a respective pair of electrode sets.

In the present embodiment, the agitation of the electrolyte, workpieces and carbon particles is carried out by a fluid stream and the bottom 1643a of the vessel may thus be provided with a plurality of liquid inlets 1623a, 1623b, 1623c, 1623n forming electrolyte jets oriented generally tangentially to an imaginary circle C centered upon the vertical axis of the chamber and tangential as well to the curvature of the floor of the vessel as will be apparent from FIGS. 8 and 9. These inlets individually extend through the vessel 1610 and communicate via lines 1640a, etc. with a pump 1639 drawing QlQGtrolyte from the reservoir 1644. Electrolyte is returned to the reservoir via a line 1643'. Each of hese lines is provided with a respective electromagnetically operable valve 1659a etc. which successively pulse the electrolyte jets introduced into the vessel. Consequently, a vortex agitation of the electr'olytefis provided which dynamically coacts with gravitational force to produce the desired turbulence. When more turbulence is desired, the jets can be pulsed in random sequence rather than in succession as indicatedgThe deburring electrolyte may be admixed with inert gas(see FtlGQ from a cylinder 1650 and a valve 1650a whichmay be injected into the electrolyte stream or may be added exclusively through one of the inlet passages (i.e. passage 1623;: in the system of FIGS. 8 and 9).

EXAMPLE H A seriesof comparative tests were carried out with the stationary vessel arrangements of FIGS. 8 and 9, with a rotary vessel system and with a vibratory vessel system as described below. The electrolyte was an aqueous solution of 15% by weight of potassium nitrite and the workpieces were hexagonal nuts composed of iron and of 8 mm. diameter. The nuts were of first grade 115 standard, black, class 4 M8SS41B-D with a total volume of 500 cc. The deburring elements added to the system were carbon particles of .15 mm. diameter or abrasive particles of alumina or silica, each of 15 mm. diameter. When particles were added, atotal quantity of 2000 cc. of such particles were used. The rotary system involved 55 drum revolutions per minute, the vibratory system applied drum vibrations of 1500 cycles per minute and the jet system made useof an electrolyte pressure of 5 and 15 kg. per cm. Four jets were employed in each case and the following tables give the total quantity of material removed in thedeburring process, the voltage and amperage provided for the electrochemical action and the particle wear in percents by weight. The deburring operation for each case was carried out equally for minutes.

1.-ROTARY SYSTEM 3.J' ET SYSTEM (with 5 kg./cm. electro1yte pressure) (a) Carbon only 90 4 (b) Carbon (50) A1203 (50) (c) A1203 (50), iOz (50) '62 45 0.2 26

' if-J ET SYSTEMtwith kg./em. electrolyte pressure) (a) Carbon only l5 100 3 56 (1)) Carbon (50), A1203 (50) 43 62 4 39 203 (50); SiO2 In addition, an electromagnet 1615 may be provided below the vessel as shown in FIG. 8 to augment the dynamic movement produced by the liquid jets by electromagnetically induced movementsIIt will also be under's'tood that various combinations of the several systems may be provided as well; Thus, the systems of FIGS. 1, 5 and6 may provide" pulsed electrolyte jets to increase agitation while similar jets "may be provided in the system of FIG. 7. A conveyor belt may be passed through the vessel of FIG. 8. The vessel of FIG. 8 may also be vibrated by electromagnetic means as shown in FIG. 7 or may co-operate with angularly oscillatable and vertically reciprocable electrodes as there shown.

"In FIG. 10, I show a system for the deburring of metallic workpieces which comprises an upwardly open vessel '1710xcontaining' metallic workpieces 1712 and graphite particles 1713 ;inana electrolyte generally repre.'

sented at 1711. The vessel is supported resiliently, e.g. by springs 1724 upon a base 1724a and is provided with a mechanical or electromagnetic vibrator 1715 of the type previously described. Within the vessel, pairs of electrodes 1717a, 1717b and 1718a and 1718b are juxtaposed across the deburring region and are separated from the mass of particles and workpieces by nonconductive and mechanically strong screens 1717' and 1718'. The electrodes 1717a, 1717b and 1718a, 1718b are connected to common poles of a direct-current source 1719 via a reversing switch 1719a, 1719b, the electromagnetic actuators of which are operated by a timer 17190 to periodically reverse the polarities of the electrodes and measure uniform deburring.

The conductive particles 1713 are preferably graphite, as noted earlier, but may include silicon carbide, boron carbide or like abrasives or may be accompanied in the mass by abrasive particles of similar size.

Above the vessel 1710, I provide a dispenser 1740 with an electromagnetic valve 1740a controlling the supply of electrolyte from a reservoir 1744. Electrolyte may in part be recirculated from the outlet 1743 of the vessel to the reservoir 1744 as described, for example, in connection with FIG. 7. A current-responsive means in the form of a resistor 1740b in series with the source 1717 and one of the electrode pairs 1718a, 1718b, produces a signal which is detected and amplified at 17400 to control the valve 1740a. In addition, a timer may be provided for periodic opening of valve 1740 to feed electrolyte to the system. However, it has been found desirable, as noted earlier, to limit the proportion of electrolyte to the conductive particles and thus I prefer to use the electrolyte sensor of FIG. 10 to provide the minimum additional electrolyte necessary for deburring. It will be understood that the electrolyte within the vessel tends to become depleted by reason of electrolyte decomposition and evaporation. As a result of such depletion, there is a change in the resistance across the vessel, corresponding to a change in the current flow through resistor 1740b and modification of the voltage drop thereacross. As soon as the electrolyte content of the vessel falls, replacement electrolyte is added.

At the base of the vessel, I provide a screen or perforated plate 1743a with openings smaller than the sizes of the particles and workpieces to enable contaminated electrolyte to be drained through the screen 1743a. This system has an advantage in that large electrolyte volumes in some cases co-operate with workpieces of a particular configuration to prevent true random movement of the workpieces in the electrode.

In the foregoing, I have described batch processing of workpieces b random movement of the workpieces and the conductive particles in a tumbling drum or a container and also the somewhat controlled deburring of workpieces carried by a conveyor through an electrolyte. In the latter case, it is not always possible to remove the workpieces in the order in which they are introduced into the system. Such removal may be desirable from time to time and I have found that it is possible to achieve this result by tumbling the workpieces On a continuous carrier. i In FIGS. 11-14, I show an apparatus capable of processing the workpieces continuously with the advantages of a tumbling system and yet the advantages of a continuous through-flow arrangement. ln this system, the:-

vess'el 1810 is formed with a helical upwardly extending duct or passage 1810:: which communicates with the interior of the vessel at an opening 1810b toward thebottom thereof. The vessel 1810 is mounted resiliently by springs 1824 as shown diagrammatically in FIG. 12 but in structural terms in FIG. 13. In this figure, the springs 1824 are shown to be resilient blades anchored at 1824:: to a pedestal 1824b and supporting the vessel 1810 at 18240. An electromagnetic coil 1815 is provided on the pedestal 1824b and is juxtaposed with an armature 1815a carried by the vessel 1810 A..periodic -current source. 

